Both are studies of the mind. Psychiatrists are psychologists with an M.D. degree.
Psychology: http://en.wikipedia.org/wiki/Psychology
Quote: "an academic and applied discipline that involves the scientific study of mental functions and behaviors"
Psychiatry: http://en.wikipedia.org/wiki/Psychiatry
Quote: "the medical specialty devoted to the study, diagnosis, treatment, and prevention of mental disorders."
See the word "mental" in both definitions? Neither studies the brain, neither is scientific, and the distinction between them is more a matter of history than topic.
I ask that you think about what you're saying. If human psychology were a science, then its two major subfields, psychiatry and psychology (there are actually 54, but never mind), would be looked on as intimately related to human psychology and to each other.
Would you argue that cosmology and particle physics aren't related to each other because they study different things, i.e. one studies the universe at the largest possible scale and the other at the smallest? Most scientists would disagree because these two fields rely on physics and physical theory for their scientific standing.
> but it applies to psychiatry (more specifically, the DSM) rather than to psychology.
False. Both psychiatry and psychology rely on the DSM as a diagnostic guide.
Link: http://www.psychiatry.org/practice/dsm
Title: "DSM"
Quote: "The Diagnostic and Statistical Manual of Mental Disorders (DSM) is the standard classification of mental disorders used by mental health professionals in the United States ... It can be used by a wide range of health and mental health professionals, including psychiatrists and other physicians, psychologists, social workers, nurses, occupational and rehabilitation therapists, and counselors. "
> I agree with your major point, but it applies to psychiatry (more specifically, the DSM) rather than to psychology.
On the contrary, it applies to both, because both psychiatry and psychology depend on the DSM's imagined authority for diagnosis and treatment guidance.
If the DSM were to suddenly disappear, psychologists would have no therapeutic guidebook. That wouldn't stop them, of course, but it would be disrupting and embarrassing.
If human psychology were a science, we wouldn't be having this conversation, because psychiatry and psychology would be looked on as branches of a science with more similarities than differences, just as with cosmology and particle physics.